This invention relates to flame retardant polyurethane foams. More particularly, it relates to flexible polyurethane foams which are flame retardant and, additionally, when subjected to combustion temperature are substantially dripless, forming a char during combustion. The flexible polyurethane foams comprise in addition to suitable diisocyanates, polyols, and additives, a flame retardant material and a polyol having hydroxyl groups which are substantially non-reactive with the diisocyanate component of the foam-forming formulation during the course of the foam-forming reaction.
The desirability of flame retardant foams for many applications has been recognized. Efforts have been made to render flexible polyurethane foams flame retardant by the addition of various compounds to the basic composition used to produce cellular foam products. These compounds include both organic and inorganic materials containing in their molecular structure the elements phosphorus, antimony, boron; and the halogens such as chlorine and bromine. Additionally, in providing flame retardant foams efforts have been made to chemically bond within the foam-forming polyol, such as the polyester and polyether polyols, large hydroxyl group containing molecules including starch, glucose, and the like. These efforts have been directed to rigid foams and not flexible foams. While flexible polyurethane foams produced in accordance with prior art techniques will meet certain flammability standards, the foams produced are characterized during combustion by undesirable melting and dripping of the cellular structure. The molten material can be hazardous due to its uncontrolled transport or flow from the site of the flames to surrounding or underlying surfaces. Moreover, it has been found that conventional flame retarding techniques often result in foams which are unduly soft, precluding the manufacture of clickable foams.
More recently, the reduction or elimination of melting and dripping characteristics in flexible foams as noted above, in addition to flame retardant properties, has been emphasized by the industry. The non-dripping characteristic is not only desirable from the standpoint of reducing the hazards of flaming droplets, but is critical from the standpoint of safety in certain applications where the melting and dripping of the foam provides a substantial hazard to the public as a result of the extreme heat of the droplets formed. In an effort to eliminate dripping of the molten material, it has been suggested that the level of flame retardants incorporated into the polyurethane foaming composition, particularly the phosphorus and antimony base compounds, be substantially increased. Although this method has met with limited success, the flexible foams produced are substantially more costly due to the high cost of the flame retardant and, further, the presence of the larger quantities of flame retardants within the polyurethane polymer results in poorer physical properties, particularly a lower level of firmness. Further, it is often difficult to control the foaming and polymerization reaction. It is, therefore, necessary from a practical standpoint to limit the amount of flame retardant material used.